I don't know if I would suggest powering all four interior speakers and a sub with one four channel amp......I guess it could be done, as some of the more expensive/complex amps are capable of doing so, but it is not typical (or the most efficient/productive way to use an amp) IMO. If you wanted to power all the interior speakers (4 speakers) as well as a sub, I would suggest either a five channel amp or multiple amps (four channel amp for the interior speakers and either a mono amp or a two channel amp for the sub). Admittedly, there are flaws in every "rule", or school of thought, but to keep things simple, this is what I would suggest.